There is a name for what happens to a person who receives a very large dose of radiation and still, for a while, seems fine. Doctors call it the latent phase. Online, it has a darker nickname: the walking ghost.
Hisashi Ouchi is the man most people think of when they hear it. He was 35, a technician at a nuclear fuel plant in the village of Tokaimura, about two hours north-east of Tokyo. On the morning of 30 September 1999 he was standing over a tank when it reached criticality. He lived for 83 more days.
This is not a ghost story, though it’s often told like one. It’s a story about a shortcut.
The bucket method
The plant was run by JCO, a company that prepared uranium fuel. That day, Ouchi and two colleagues were making a batch for an experimental reactor, using uranium enriched to 18.8%. That’s far richer than the fuel the plant usually handled, and the crew had no real training for it.
The approved process used dedicated equipment designed to keep the material in safe, small amounts. Instead, the workers dissolved the uranium in stainless-steel buckets and poured it by hand into a precipitation tank that was never meant to hold that much. A version of this shortcut had been used at the plant for about three years, without the regulator’s permission.
At about 10:35 that morning, with roughly 16 kg of uranium in the tank, the solution went critical. The workers saw a blue flash. Alarms sounded. The chain reaction didn’t stop on its own; it carried on, on and off, for about 20 hours, until crews drained cooling water from around the tank and added boric acid to kill it.
Three men, three doses
Radiation doses are measured in grays (Gy). Ouchi, closest to the tank, was estimated to have received around 16 to 20 Gy. His colleague Masato Shinohara, who had been helping pour, received around 6 to 10 Gy. Their supervisor, Yutaka Yokokawa, sitting at a desk further from the tank, received a much smaller dose and survived.
For comparison, a dose of a few grays can be fatal without treatment. Ouchi’s was many times that.
Eighty-three days
Ouchi was flown to a specialist hospital in Tokyo. For the first days he could talk, and to visitors he looked far less sick than he was. That’s the latent phase, and it’s why the “walking ghost” label stuck. The radiation had already done the damage at a cellular level; his body simply hadn’t shown it yet.
What followed was weeks of intensive, experimental treatment, including transfusions and a stem-cell transplant, as doctors tried to rebuild what the radiation had destroyed. His family stayed close throughout. He died on 21 December 1999, the first person in Japan to die from a nuclear accident. Shinohara died in April 2000.
You’ll find graphic descriptions and photos of his treatment online. We don’t share them here, and we’d gently suggest you don’t go looking. He was a person, not a cautionary image.
What it changed
- 161 people living within 350 metres were evacuated, and around 300,000 people within 10 km were told to stay indoors for about a day.
- The accident was rated Level 4 on the international nuclear event scale, an accident with local consequences.
- JCO lost its licence to operate. Company officials and staff were later prosecuted, and several were convicted.
- The investigations exposed a secret procedure manual that had sanctioned the shortcut, and led to tighter inspection of fuel facilities in Japan.
Why we told it as our 800th
A milestone episode felt like the right place for a story that sits in the uneasy space between true crime and horror. Nobody set out to hurt anyone at Tokaimura. That’s exactly what makes it frightening: a handful of small decisions, each one saving a bit of time, adding up to something nobody could undo.
If you’re drawn to the darker side of real Japanese history, our Japanese True Crime guide collects the cases we’ve covered, from Futoshi Matsunaga to the unsolved Setagaya murders.
Sources: Tokaimura Criticality Accident 1999 (World Nuclear Association); Tokaimura nuclear accident (Wikipedia).
